It’s a rare theatrical evening indeed, when the most unexpected combination of disciplines create a chemical reaction that explodes inside your heart.

That’s the case in “Constellations,” the Nick Payne romantic comedy/drama that was opened by All In Productions Friday night at the Tenth Street Theatre.

With two superb actors, marvelously taut direction and a play that marries science with love, it is truly a must see for any theater fan before it closes its brief fun next Sunday.

Boy meets girl – him from one world and her from another – is perpetually the stuff that stories are crafted from. But this is nothing like the other boy meets girl trope that you’ve seen.

This is the story of Marianne (Libby Amato) and Roland (David Sapiro). But rather than telling it from start to finish in a world of reality Payne has crafted a story told with a nod to the string theory of physics.

“In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. It describes how these strings propagate through space and interact with each other.”

In case that kind of thing gives you the shivers, don’t worry about it. This most entertaining of productions is as romantic, touching and funny as you could imagine. In short, it’s kind of like a real relationship.

When first we see them, the two meet at a barbecue, and it is Marianne who is obviously searching for a hookup of some kind.

She spots Roland and leads with her best line.

“Do you know why it’s impossible to lick the tips of your elbows? They hold the secret to immortality, so if you COULD lick them, there’s a chance you’d be able to live forever. But if everyone did it, if everyone could actually lick the tips of their elbows, then there’d be chaos. Because you can’t just go on living and living and living.”

Roland replies that he’s in a relationship and Marianne moves on. She tries the same thing on a married Roland and another married Roland. Finally, she finds a Roland who is unmarried and interested.

He is a beekeeper and she is a theoretical physicist. The odd couple has nothing on these two.

But there are – more than one Mariannes and more than one Rolands. They are particles in a universe where every decision and action steers each of them in one direction or another.

Payne calls this the multiverse.Marianne Tries to explain it to Roland upon their first meeting.

Marianne: Let’s say that ours really is the only universe that exists. There’s only one unique me and one unique you. If that were true, then there could only ever really be one choice. But if every possible future exists, then the decisions we do and don’t make will determine which of these futures we actually end up experiencing. Imagine rolling a dice six thousand times.

Roland But if everything I’m ever gonna do already exists, then what’s the point in me –

Marianne There isn’t. Roland What?

Marianne In none of our equations do we see any sign whatsoever of any evidence of free will.

Roland In your e-

Marianne We’re just particles. Roland Speak for y’self.

Marianne You, me, everyone, we might think that we have some say in – We might think that the choices we make will have some say in the –

Roland Right, no, sure – Marianne We’re just particles –

Roland No, sure, but –

Marianne We’re just particles governed by a series of very particular laws being knocked the fuck around all over the place.

Roland You make it sound so glamorous.

The structure of this play is unusual in that each scene between Marianne and Roland is replayed and replayed again.

Director Mitch Weindorf moves the two actors around the stage, just slightly, signaling that we are going to see something new or at least newish.

We follow Marianne and Roland through their relationship, courting, marriage, the crisis of cheating, forgiveness and the moment they face mortality.

This production wouldn’t work at all if it wasn’t for the absolutely outstanding work of the two actors. The play would be hard to follow and lead to an early tune out for many in the audience. But this one was riveting, from beginning to end.

Ms. Amato isn’t seen nearly enough on Milwaukee stages and this performance is an eloquent example of what she brings to a stage. She is immaculately delicate and precise in capturing the kind of awkward emotional and physical manifestations of a nerd in love .

Five years ago she dazzled this same theater with Mary C. McLellan in a stunning performance of “The Nightmare Room,” staged by In Tandem. She is no less stunning here.

Mr. Sapiro continues his steady climb up the ladder of Milwaukee actors who can find surprising depth in a character. He is both dumbfounded and remarkably perceptive in his various personna. His gentleness and love and support for Marianne is steadfast, despite the boulders thrown in their path.

Perhaps the most mesmerizing scene in the entire play is when the two repeat a scene just played, but in a kind of silent sign language that owed something to sign language for the deaf and something unique to this discussion.

It’s a moment that must be seen to be appreciated and these two actors have a special kind of chemistry that enwraps the stage and the audience.